Her hands and arms have long been riddled with them, but now bulging veins are even popping up on Madonna's face.

The star emerged from yet another workout with a bizarre zig-zag vein throbbing from her temple, a sign she may be taking her punishing workouts too far.

The Queen of Fitness is famous for enduring two-hour sessions six days a week, and strenuous exercise is known to increase the blood flow which makes veins bigger.

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Eye popping: a thick vein was bulging from Madonna's temple after yet another workout at her personal gym in London today

And today it appears she's worked out extra hard, spurred on by the presence of her best pal turned training buddy Gwyneth Paltrow.

The actress, who has just returned from a visit to New York, joined health fanatic Madonna on a morning workout at the pop star's £6million personal gym, which is just 20 yards from her front door.

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Trim and trimmer: Gwyneth, who recently returned from New York, joined the star for a workout

It was, after all, Gwyneth who found her first.

After giving birth to baby Moses in 2006, the health-conscious actress was confronted with a weight gain of more than 2 1/2st.

Following a strict diet, the star managed to shift half of it within several weeks, but that last stone proved to be impossible; and for months she resorted to wearing two Spanx girdles at a time.

With the start date for her film, Iron Man, fast approaching, Gwyneth made a last-ditch attempt to get her body into shape, and called on Tracy.

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Training day: the pair walked 20 yards from Madonna's home to her £6million gym next door

Tracy has now been working with Madonna, who turns 50 in August, six days a week for the past year.

Madonna and Gwyneth share more than just a desire to be in great shape - earlier this year Gwyneth apparently began exploring Kabbalah, the branch of Jewish mysticism the singer follows.

Gwyneth, who last week denied her marriage to Coldplay star Chris Martin is in trouble, was spotted leaving a New York Kabbalah Centre earlier this year.

A source told Mail Online at the time: "She's a seeker, and with Madonna's encouragement, she's now looking into Kabballah - she's simply on a personal quest."

Guru: the duo were joined by Madonna's personal trainer Tracy Anderson